Characterization of nighttime formation of particulate organic nitrates based on high-resolution aerosol mass spectrometry in an urban atmosphere in China

Abstract

Abstract. Organic nitrates are important atmospheric species that significantly affect the cycling of NOx and ozone production. However, characterization of particulate organic nitrates and their sources in polluted atmosphere is a big challenge and has not been comprehensively studied in Asia. In this study, an aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed at an urban site in China from 2015 to 2016 to characterize particulate organic nitrates in total nitrates with a high time resolution. Based on the cross-validation of two different data processing methods, organic nitrates were effectively quantified to contribute a notable fraction of organic aerosol (OA), namely 9 %–21 % in spring, 11 %–25 % in summer, and 9 %–20 % in autumn, while contributing a very small fraction in winter. The good correlation between organic nitrates and fresh secondary organic aerosol (SOA) at night, as well as the diurnal trend of size distribution of organic nitrates, indicated a key role of nighttime local secondary formation of organic nitrates. Furthermore, theoretical calculations of nighttime SOA production of NO3 reactions with volatile organic compounds (VOCs) measured during the spring campaign were performed, resulting in three biogenic VOCs (α-pinene, limonene, and camphene) and one anthropogenic VOC (styrene) identified as the possible key VOC precursors to particulate organic nitrates. The comparison with similar studies in the literature implied that nighttime particulate organic nitrate formation is highly relevant to NOx levels. This study proposes that unlike the documented cases in the United States and Europe, modeling nighttime particulate organic nitrate formation in China should incorporate not only biogenic VOCs but also anthropogenic VOCs for urban air pollution, which needs the support of relevant smog chamber studies in the future.

Summertime aerosol volatility measurements in Beijing, China

“…The Weather Research and Forecasting -Chemistry (WRF-Chem, version 3.7.1) model was used to simulate the volatility distribution of SOA in the summer of 2017. The detailed physical and chemical schemes have been given in Zhang et al (2019). As shown in Fig.…”

“…Therefore, semi-volatile and intermediate-volatility organic compound emissions in China are too limited to be used in SOA simulations (Liu et al, 2017). In addition, model underestimation of atmospheric oxidation capacity, especially in polluted areas, due mainly only to the inclusion of the key gas-phase production of HONO in air quality models (Sarwar et al, 2008;Li et al, 2010Li et al, , 2011Zhang et al, 2019), and few volatility bins used in WRF-Chem, especially for volatility bins of less than 1 µg m −3 at 300 K, all contributed to the discrepancies between model simulation and observations.…”

Efficient Nighttime Biogenic SOA Formation in a Polluted Residual Layer

“…As NO 3 concentration depends on the availability of NO x , a substantial fraction of the biogenic SOA formed at night is controlled by anthropogenic emissions, as has been observed and predicted in several regions across the United States, Europe, and China (Ayres et al, 2015; Brown et al, 2013; Fry et al, 2018; Kiendler‐Scharr et al, 2016; Pye et al, 2015; Rollins et al, 2012; Yu et al, 2019; Zaveri et al, 2010). We report here on nighttime biogenic SOA formation in a polluted residual layer over Sacramento, California, during the Carbonaceous Aerosols and Radiative Effects Study (CARES) in June 2010 (Zaveri et al, 2012).…”

Estimation of particulate organic nitrates from thermodenuder-aerosol mass spectrometer measurements in North China Plain

“…One of the major uncertainties is that R ON varies largely depending on reaction conditions and precursors in ambient rather than being constant values. In some environments, the measured ratio of NO + to NO 2 + in ambient is even lower than the average ratio of NO + to NO 2 + from ammonium nitrate (R AN ), resulting in negative values of pON estimated by the "NO x method", especially for the wintertime in China when aerosol particles are dominated by inorganic nitrate (Yu et al, 2019;Zhu et al, 2016).…”

“…Recently, pON were also quantified using high-resolution aerosol mass spectrometer (HR-AMS) mainly based on the differences of fragmentation patterns between pON and inorganic nitrate (Xu et al, 2015b;Farmer et al, 2010;Kortelainen et al, 2017;Ng et al, 2017). "PMF method" and "NO x method" are two most commonly used method for pON quantification (Fry et al, 2013;Xu et al, 2015b;Yu et al, 2019;Dai et al, 2019). The "PMF method" by combining organic and inorganic fragments in positive matrix factorization (PMF) analysis was able to identify organic aerosol factors that showed largely different NO + /NO 2 + ratio from pure ammonium nitrate (AN).…”